1. Field of the Invention
This invention relates to structures of thin film magnetic write heads. More specifically, the invention relates to structures of a thin film write heads for thermally assisted, dual gradient recording, wherein a portion of the magnetic write pole is integrated into the structure of an optical aperture, the aperture serving as ridge waveguide near field optical source.
2. Description of the Related Art
The ongoing quest for higher storage bit densities in magnetic media used in, for example, hard disk drives, have reduced the size (volume) of data cells to the point where the cell dimensions are limited by the grain size of the magnetic material. Although grain size can be reduced further, there is concern that data stored within the cells is no longer thermally stable, as random thermal fluctuations at ambient temperatures are sufficient to erase data. This state is described as the superparamagnetic limit, which determines the maximum theoretical storage density for a given magnetic media. This limit may be raised by increasing the coercivity of the magnetic media or lowering the temperature. Lowering the temperature is not a practical option when designing hard disk drives for commercial and consumer use. Raising the coercivity is a practical solution, but requires write heads employing higher magnetic moment materials, or techniques such as perpendicular recording (or both).
One additional solution has been proposed, which employs heat to lower the effective coercivity of a localized region on the magnetic media surface; writes data within this heated region with a broad magnetic field; and, “fixes” the data state by cooling the media to ambient temperatures. This technique is broadly referred to as “thermally assisted (magnetic) recording”, TAR or TAMR. It can be applied to both longitudinal or perpendicular recording systems, although the highest density state of the art storage systems are more likely to be perpendicular recording systems. Heating of the media surface is accomplished by a number of techniques such as focused laser beams or near field optical sources.
FIG. 6 (Prior Art) is a chart 600 of field strength H as a function of position on the media for conventional thermally assisted recording. An optical source is projected onto the media surface, creating a heated zone 608. Within this zone, the coercivity Hk of the media changes in accordance with curve 602, wherein the lowest coercivity occurs at the hottest point within the heated zone 608. Surrounding the heated zone is an applied magnetic field of strength Heff curve 604. Although the broad field Heff determines the value of the data bit being written, the data is not “fixed” on the media until the media temperature falls below a particular value, where Hk equals Heff, the recording point 606. For state of the art high density recording applications, the position of this recording point must be known as accurately as possible. This may be partially accomplished by reducing the size of the heated zone as much as possible, but variations in the magnetic and thermal properties of each magnetic grain (or cluster) can still result in variations between the intended magnetic transition position and the actual position. This position “jitter” can subsequently produce data errors.
What is needed is an improved method for thermally assisted recording.